1. Field of the Invention
The present invention relates generally to macromolecule compositions and methods for their preparation and use. In particular, the present invention relates to a method for preparing macromolecule compositions by spray drying under controlled conditions which preserve protein purity and results in good powder dispersibility and other desirable characteristics.
Over the years, certain drugs have been sold in compositions suitable for forming a drug dispersion for oral inhalation (pulmonary delivery) to treat various conditions in humans. Such pulmonary drug delivery compositions are designed to be delivered by inhalation by the patient of a drug dispersion so that the active drug within the dispersion can reach the lung. It has been found that certain drugs delivered to the lung are readily absorbed through the alveolar region directly into blood circulation. Pulmonary delivery is particularly promising for the delivery of macromolecules (proteins, polypeptides, high molecular weight polysaccharides, and nucleic acids) which are difficult to deliver by other routes of administration. Such pulmonary delivery can be effective both for systemic delivery and for localized delivery to treat diseases of the lungs.
Pulmonary drug delivery can itself be achieved by different approaches, including liquid nebulizers, aerosol-based metered dose inhalers (MDI""s), and dry powder dispersion devices. Aerosol-based MDI""s are losing favor because they rely on the use of chlorofluorocarbons (CFC""s), which are being banned because of their adverse effect on the ozone layer. Dry powder dispersion devices, which do not rely on CFC aerosol technology, are promising for delivering drugs that may be readily formulated as dry powders. Many otherwise labile macromolecules may be stably stored as lyophilized or spray-dried powders by themselves or in combination with suitable powder carriers.
The ability to deliver pharmaceutical compositions as dry powders, however, is problematic in certain respects. The dosage of many pharmaceutical compositions is often critical, so it is desirable that dry powder delivery systems be able to accurately, precisely, and reliably deliver the intended amount of drug. Moreover, many pharmaceutical compositions are quite expensive. Thus, the ability to efficiently formulate, process, package, and deliver the dry powders with a minimal loss of drug is critical. While the permeability of natural macromolecules in the lung is well known, the combined inefficiencies of macromolecule production processes and macromolecule delivery has limited commercialization of dry macromolecule powders for pulmonary delivery.
A particularly promising approach for the pulmonary delivery of dry powder drugs utilizes a hand-held device with a hand pump for providing a source of pressurized gas. The pressurized gas is abruptly released through a powder dispersion device, such as a venturi nozzle, and the dispersed powder made available for patient inhalation. While advantageous in many respects, such hand-held devices are problematic in a number of other respects. The particles being delivered are usually less than 5 xcexcm in size, making powder handling and dispersion more difficult than with larger particles. The problems are exacerbated by the relatively small volumes of pressurized gas, which are available using hand-actuated pumps. In particular, venturi dispersion devices are unsuitable for difficult-to-disperse powders when only small volumes of pressurized gas are available with the handpump. Another requirement for hand-held and other powder delivery devices is efficiency. High device efficiency in delivering the drug to the patient with the optimal size distribution for pulmonary delivery is essential for a commercially viable product. Conventional techniques used to deliver medication do not have the delivery efficiency required for commercialization. The ability to achieve both adequate dispersion and small dispersed volumes is a significant technical challenge that requires that each unit dosage of the powdered composition be readily and reliably dispersible.
Spray drying is a conventional chemical processing unit operation used to produce dry particulate solids from a variety of liquid and slurry starting materials. The use of spray drying for the formulation of dry powder pharmaceuticals is known, but has usually been limited to small molecule and other stable drugs which are less sensitive to thermal degradation and other rigorous treatment conditions. The use of spray drying for the preparation of biological macromolecule compositions, including proteins, polypeptides, high molecular weight polysaccharides, and nucleic acids, can be problematic since such macromolecules are often labile and subject to degradation when exposed to high temperatures and other aspects of the spray drying process. Excessive degradation of the macromolecules can lead to drug formulations lacking in the requisite purity. It can also be difficult to control particle size and particle size distribution in compositions produced by spray drying. For pulmonary delivery, it is critical that the average particle size be maintained below 5 xcexcm, preferably in the range from 0.4 xcexcm to 5 xcexcm, and that the amount of the composition comprising particles outside of the target size range be minimized. Preferably, at least 90% by weight of the powder will have a particle size in the range from 0.1 xcexcm to 7 xcexcm. More preferably, at least 95% will have a size in the range from 0.4 xcexcm to 5 xcexcm. Moreover, it can sometimes be difficult to achieve a desired low moisture content required for physical and chemical stability in the final particulate product, particularly in an economic manner. Finally, and perhaps most important, it has been difficult to produce the small particles necessary for pulmonary delivery in an efficient manner. For high value macromolecular drugs, collection efficiencies (i.e., the amount of particulate drug recovered from the process in a useable form) should be above 80% by weight, preferably above 90% by weight, and desirably above 95% by weight. While spray drying has been used to prepare powder of macromolecules in laboratory scale equipment as described below, commercial spray driers are not designed to produce powders in the pulmonary size range. The methods for atomization, drying powder, and collection must be modified to economically produce a protein powder with the desired product characteristics for pulmonary delivery and in sufficient yield and at commercially acceptable production rates (in excess of 30 g/hr).
It is therefore desirable to provide improved methods for the spray drying of macromolecules for use in pulmonary and other drug delivery. In particular, it is desirable to provide improved process methods and powder composition which address at least some of the deficiencies listed above.
2. Description of the Background Art
U.S. Pat. Nos. 5,260,306, 4,590,206, GB 2 105 189, and EP 072 046 describe a method for spray drying nedocromil sodium to form small particles preferably in the range from 2 to 15 xcexcm for pulmonary delivery. U.S. Pat. No. 5,376,386, describes the preparation of particulate polysaccharide carriers for pulmonary drug delivery, where the carriers comprise particles sized from 5 to 1000 xcexcm and having a rugosity less than 1.75. Mumenthaler et al., (1994) Pharm. Res. 11:12 describes recombinant human growth hormone and recombinant tissue-type plasminogen activator. That study demonstrated that the proteins may degrade during spray drying and hence may not retain sufficient activity for therapeutic use. WO 95/23613 describes preparing an inhalation powder of DNase by spray drying using laboratory-scale equipment. WO 91/16882 describes a method for spray drying proteins and other drugs in liposome carriers.
The following applications assigned to the assignee of the present application each describe that spray drying may be used to prepare dry powders of biological macromolecules: application Ser. No. 08/423,515, filed on Apr. 14, 1995; application Ser. No. 08/383,475, now abandoned, which was a continuation-in-part of application Ser. No. 08/207,472, filed on Mar. 7, 1994; now abandoned application Ser. No. 08/472,563, filed on Apr. 14, 1995, now abandoned, which was a continuation-in-part of application Ser. No. 08/417,507, filed on Apr. 4, 1995, now abandoned, which was a continuation of application Ser. No. 08/044,358, filed on Apr. 7, 1993, now abandoned; application Ser. No. 08/232,849, filed on Apr. 25, 1994, now U.S. Pat. No. 5,607,915, which was a continuation of application Ser. No. 07/953,397, now abandoned. WO 94/07514 claims priority from Ser. No. 07/953,397. WO 95/24183 claims priority from Ser. Nos. 08/207,472 now abandoned, and 08/383,475, now abandoned.
According to the present invention, methods for spray drying biological macromolecules provide pharmaceutical compositions having improved characteristics which overcome at least some of the deficiencies noted above with respect to prior spray drying processes. The methods of the present invention comprise providing a predetermined concentration of the macromolecule and optionally other excipients as a solution, slurry, suspension, or the like, in a liquid medium, usually in water as an aqueous solution. The macromolecule is optionally formulated in solution with compatible excipients such as sugars, buffers, salts, and other proteins, as needed to provide a therapeutically effective dose, inhibit degradation during drying, promote powder dispersibility, and achieve acceptable physical and chemical stability of the powder at room temperature. The liquid medium is atomized under conditions selected to form droplets having an average particle size at or below a predetermined value, and the droplets are then dried under conditions selected to form particles of the formulation having a moisture content below a predetermined threshold level. The dried particles are collected and packaged in a form suitable for use, typically in a unit dosage receptacle. The conditions of atomizing and drying will preferably be selected so that the particles may be dried below the target moisture content in a single drying step, and so that the particles are produced in the desired size range without having to further separate (e.g., size classify) the particles prior to packaging.
In a first preferred aspect of the method of the present invention, the total solids content in the liquid medium (including the macromolecule and excipient(s)) will be below 10% usually being in the range between 0.5% and 10% wt. Preferably, the concentration will be in the range from about 1% wt to 5% wt, and the liquid medium will comprise an aqueous solution. It has been found that control of the concentration of the total solids below 5% significantly enhances the ability to obtain dried particles in the desired size range, i.e., below 5 xcexcm, and preferably in the range from 0.4 xcexcm to 5 xcexcm.
In a second preferred aspect of the method of the present invention, the solution is atomized to produce droplets having a median droplet size at or below 11 xcexcm. Optimization of the atomizer design and operating conditions allows the solids content to be increased to the levels described above making high volume production practical and economical. Preferably, the atomization step is performed by flowing the solution and an atomization gas stream through a two-fluid nozzle at a predetermined gas:liquid mass flow ratio, preferably above 5. The air pressure upstream of the air orifice is maintained above 25 psig. While such air pressure is above that which results in sonic velocity, i.e., the velocity does not continue to increase above sonic velocity, it has been found that increased density of the higher pressure atomization gas decreases the droplet size produced.
In another aspect of the method of the present invention, the atomized droplets are dried to form particles having a final moisture content below 5% by weight. Preferably, the particles are dried to this level in a single drying operation, typically within a single spray drying operation where the droplets are flowed concurrently with a heated gas stream having sufficient heat energy to evaporate water in the particles to the desired level before the particles are collected from the drying operation. Usually, the heated gas stream, typically a heated air stream, will have an inlet temperature of at least 90xc2x0 C., preferably being at least 120xc2x0 C., more preferably being at least 135xc2x0 C., and still more preferably being at least 145xc2x0 C., and often being 175xc2x0 C., or as high as 200xc2x0 C. depending on the macromolecule being dried. At least in part, the inlet temperature of the heated gas drying stream will depend on the lability of the biological macromolecule being treated. In the exemplary case of insulin, an inlet temperature in the range from 140xc2x0 C. to 150xc2x0 C. is preferred.
In order to control the final moisture content of the particles produced in the drying operation, it is desirable to also control the gas outlet temperature. The gas outlet temperature will be a function of the inlet temperature, the heat load imposed by the product drying step, (which depends on the inlet temperature of the liquid medium, the quantity of water to be evaporated, and the like), and other factors. Preferably, the gas outlet temperature will be maintained at at least 50xc2x0 C. or above, preferably at at least 70xc2x0 C., usually being in the range from 60xc2x0 C. to 80xc2x0 C.
In yet another specific aspect of the method of the present invention, the drying conditions will be selected to control the particle morphology in order to enhance powder dispersibility. In particular, the drying conditions are selected to provide particles having a rugosity of at least 2. Rugosity is a measure of surface convolution, with a higher number indicating a higher degree of surface irregularity. Without intending to limit the scope of the present invention in any way, it is presently believed that the increase in surface irregularity as measured by rugosity results in a decrease in cohesiveness between adjacent particles. Such decrease in surface interactions, in turn, improves the dispersibility of the resulting powders. Particle rugosity is influenced by both the drying rate of the individual droplets and the composition of the dissolved solids.
Droplets are initially dried at a relatively high rate which will create a viscous layer of material about the exterior of the liquid droplet. As the drying continues, the viscous layer is unable to flow as rapidly as the shrinking of the particle as the solvent evaporates, resulting in surface convolutions (wrinkling) of the particles. The viscosity of the viscous layer has been related to the glass transition temperature of the material by the WLF equation (Williams, Landel, Ferry Equation) ref. K. Alexander and C. J. King, Drying Technology, Vol. 3, no. 3, 1985. The temperature gradient within the drying zone should be controlled so that the particle drying occurs sufficiently rapidly to result in the surface collapse and convolution without preceding so rapidly that the particle fractures.
In still another specific aspect of the method of the present invention, the dried particles are collected by separating substantially the entire particle output of the drying step from the gas stream. It has been found that proper control of the atomization and drying conditions can produce a dried powder having at least 90% of the mass of particles in the size range from 0.1 xcexcm to 7 xcexcm, more preferably having at least 95% in the size range from 0.4 xcexcm to 5 xcexcm, thus permitting the output of the drying step to be collected and the powder used without the need to size classify the product prior to packaging. The collected powder may then be used in any conventional manner for powder pharmaceuticals. Usually, a portion of the particle output will be packaged in a suitable container, such as a unit dosage container useful in dry powder inhalers.
In yet another specific aspect of the method of the present invention, the powder separation step will comprise passing the entire gas stream through a separator, where the separator removes at least about 90% by weight of all particles having the size of 1 xcexcm from the gas stream. The separator may comprise a high efficiency cyclone specifically designed and operated under conditions resulting in the requisite high removal efficiency for the ultrafine particles produced by the method of the present invention. Alternatively, the separator may comprise filter elements, such as a sintered metal fiber filter, a membrane filter, (e.g., a bag filter), or the like.
The methods of the present invention are useful for producing dry powders of biological macromolecules, typically macromolecules which are suitable for pharmaceutical uses, i.e., as drugs for human and veterinary purposes. Biological macromolecules include proteins, polypeptides, oligopeptides, high molecular weight polysaccharides (typically having a molecular weight above 2 kD), nucleic acids, and the like. Particular biological macromolecules are set forth in Table 1 below. The method is particularly useful for producing dry powders of insulin, which is a polypeptide hormone having a molecular weight of about 7.5 kD or above. Insulin powders prepared according to the present invention may be derived from animal sources, such as bovine insulin, or may be prepared recombinantly. Recombinant insulins may have an amino acid sequence identical to that of natural human insulin, or may be modified to some extent while maintaining the desired insulin activity.
Compositions according to the present invention comprise dispersible macromolecule powders intended for pulmonary delivery, i.e., inhalation by a patient into the alveolar regions of the patient""s lungs. The compositions comprises particles having an average particle size below 10 xcexcm and a rugosity above 2, preferably being above 3, and sometimes being above 5, usually being in the range from 2-6, preferably being in the range from 3-6, and sometimes being in the range from 4-6. Preferably, the particles of the composition will have a moisture content below 5% by weight, more preferably below 3% by weight, and typically below 2% by weight. Rugosity may be measured by BET or other conventional particle surface analysis techniques. Preferably, 90% by weight of the compositions will comprise particles having a particle size in the range from 0.1 xcexcm to 7 xcexcm, more preferably 95% in the range from 0.4 xcexcm to 5 xcexcm. The compositions will often be packaged as unit doses where a therapeutically effective amount of the composition is present in a unit dose receptacle, such as a blister pack, gelatin capsule, or the like.